1. Field of the Invention
The present invention relates to a photo-curable resin composition used to form a pattern on a substrate, and relates to a method for forming a pattern using the same.
2. Description of the Related Art
In recent years, a semiconductor integrated circuit has increasingly been made finer, and more densely integrated. To put a fine processing technology required for this purpose into practice, high accuracy photolithography equipment has been developed as a pattern transfer technology. The processing accuracy, however, has become close to the wavelength of the light source for light exposure, and thus the photolithography technology has become close to its technical limitation. As a result, instead of the photolithography technology, an electron beam drawing device, which is a type of charged particle beam device, has been used to make the processing more accurate and to fabricate a finer semiconductor integrated circuit.
In a pattern formation using an electron beam that is carried out by drawing a mask pattern, unlike in the case of a one-shot exposure method of pattern formation using a light source such as i-ray and excimer laser, there is a disadvantage that a larger number of patterns to be drawn requires a longer time of exposure (drawing), which means a longer time to form a pattern. Now the memory capacity becomes larger and larger, from 256 megabyte to 1 gigabyte and then to 4 gigabyte. This requires a drastic increase of the degree of integration, which makes the pattern density higher. A pattern with a higher density requires drastically longer time to form the pattern. Thus, a drastically lowered throughput becomes a cause for concern. In such circumstances, to increase the drawing speed of the electron beam drawing device, a one-shot irradiation drawing method has been developed. The one-shot irradiation drawing method makes it possible to form a pattern having a complicated shape, by one-shot irradiating an electron beam on the combined masks having various shapes. As a result, while a finer pattern has been made possible, the development of a large-sized and complicated electron beam drawing device has been required. This results in a disadvantage, which is an increased production cost of the device.
On the other hand, a low-cost technology for forming a fine pattern is disclosed in United State Patent Application Publication No. 5259926 (hereinafter U.S. Pat. No. 525,926), United State Patent Application Publication No. 5772905 (U.S. Pat. No. 5,772,905), S. Y. Chou et al., Appl. Phys. Lett., Vol. 67, p. 3114 (1995), and the like. In this technology, a predetermined pattern is transferred by pressing a mold having concaves and convexes arranged in the same pattern as the pattern to be formed on the substrate onto the resin film layer formed on the surface of the substrate onto which the pattern is transferred. In particular, according to the nanoimprinting technology described in U.S. Pat. No. 5,772,905 and S. Y. Chou et al., a fine structure having a fineness of not more than 25 nm can be formed by a transfer method using a silicon wafer as a mold.
The nanoimprinting technology is roughly classified into two types based on the kind of transfer receiving materials. One is a thermal nanoimprinting technology in which a transfer receiving material is heated, plastically deformed, and then cooled to form a pattern. The other is a photo nanoimprinting technology in which, after a liquid photo-curable resin is applied onto the substrate at room temperature, an optically transparent mold is pressed onto the applied resin layer, and then light is irradiated to cure the resin on the substrate, and thus, a pattern is formed. Since the pattern is formed at room temperature in the photo nanoimprinting technology, the strain caused by the difference in coefficient of linear thermal expansion between the substrate and the mold tends to be small in this technology. Thus, the photo nanoimprinting technology can be used to form a high accuracy pattern. As a result, the photo nanoimprinting technology gets a lot of attention as an alternative to the lithography technology for semiconductor and the like. As a photo-curable resin used in the photo nanoimprinting technology, PAK-01 (Toyo Gosei Co. Ltd.) is introduced in Yuichi Kurashima, Jpn. J. Appl. Phys. Vol. 42, p. 3871.
In addition, as a photo-curable resin containing acrylate, a reactive diluent, a photo reaction initiator, and a fluorochemical surfactant, a photo solder resist material is disclosed in WO No. 96-11239 and Japanese Unexamined Patent Application Publication No. Hei 7-72624 (JP 7-72624 A). The photo solder resist material has a large precure tolerance and excellent stability subsequent to precuring, and can be developed by alkali solution.
However, the photo-curable resin described in WO No. 96-11239 and JP 7-72624 A is used in patterning by the photolithography method. In the photolithography method, the patterning is done by using, in developing, the difference in solubility caused by the contrast between the area irradiated with the light and the area not irradiated. For this reason, the photo-curable resin formed on the substrate usually is cured to form a film by being pre-baked to remove the solvent after the photo-curable resin is applied onto the substrate. In photo nanoimprinting technology, however, the liquid photo-curable resin is applied onto the substrate at room temperature, and is flowed to the concave and convex portions of the mold by pressing the mold onto the liquid photo-curable resin. And then light exposure is performed to cure the photo-curable resin, and thereby a pattern is formed. Therefore, it is difficult to apply the photo-curable resin disclosed in WO No. 96-11239 and JP 7-72624 A as a resin for the photo nanoimprinting.
In addition, in a case where a high accuracy shape is patterned by photo nanoimprinting method, it is very important to make the photo-curable resin layer on the substrate as thin as possible. In other words, when the substrate is etched by dry etching method, or the like, unnecessary etching may be performed in the patterned area unless the film of the photo-curable resin is made as thin as possible in the area to be etched. This unnecessary etching may result in a reduction in patterning accuracy.
In Y. Kurashima, the photo-curable resin PAK-O1 is applied onto a quartz substrate, and then the pattern of a Si mold is transferred thereon by irradiating the light from the side of the quartz substrate while the Si mold being pressed to the resin. However, the use of the pattern formed on the photo-curable resin PAK-O1 for the purpose of processing the substrate after transferring the pattern of the Si mold to the photo-curable resin is not examined in Y. Kurashima.